The heat exchanger of the invention is of the type which surrounds a radial fan which causes the vector fluid (for example air or air and steam) to circulate and is supplied with hot gases produced by combustion of a burner.
Heat exchangers of this type are known and are constituted by a pipe, spiral-wound about the radial fan and preferably provided with internal elements which cause the fluid to spin, creating a turbulence which increases heat exchange. A burner is predisposed at one end of the pipe and is equipped with a blower to convey the hot combustion gases into the pipe. The other end of the pipe discharges directly to the environment or into a chimney flue.
Another known device, illustrated in European publication EP 0 856 705, teaches a heater constituted by a pipe, internally of which the hot gases produced by a burner flow, which pipe surrounds the fan without but not in a spiral; it is instead bent to give rise to two branches arranged side-by-side and parallel, and united by a 360.degree. free curve. This free curve absorbs heat expansion factors, so that the points where the pipe is fixed do not suffer these effects.
The above prior art realisations, however, exhibit numerous drawbacks and limitations.
One limitation is constituted by the fact that the arrangement of the pipes around the fan does not guarantee complete and sufficiently uniform coverage of the most-ventilated zone situated peripherally about the fan. This has a negative effect on the heat exchange efficiency.
Other limitations derive from the existence of a non-eptimal thermal exchange situation internally of the pipes.
The main aim of the present invention is to obviate the above-mentioned drawbacks in the prior art.